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Melanoma Study Proves Good as Gold

CancerWise -
April 2009

When extremely small particles of gold called hollow nanospheres are combined with a specific type of peptide (an amino acid compound), they can target melanoma cells and penetrate them deeply. This makes the tumor easier to destroy with near-infrared laser treatment.

"Active targeting of nanoparticles to tumors is the holy grail of therapeutic nanotechnology for cancer. We're getting closer to that goal," says Chun Li, Ph.D., the study’s senior author and professor in M. D. Anderson's Department of Experimental Diagnostic Imaging.

The research, which included laboratory and mouse studies, was published in the Feb. 1 issue of Clinical Cancer Research.

Significance of study

"There are many biological barriers to the effective use of nanoparticles, including the possibility of damage to the liver and spleen," Li says.

But this method of targeting concentrates nanoparticles near the blood vessels leading to the tumor. Less light is needed to treat the tumor, decreasing the potential for damage to surrounding tissue.

Gold was used in the study because it:

Absorbs visible and near-infrared light

Has a history of safe medical use

Background

This study is the first to look at treating tumors by combining targeted gold nanospheres and photothermal ablation, a minimally invasive treatment that uses heat generated through absorption of light to destroy target tissue. Tumors are burned with near-infrared light, which penetrates deeper into tissue than visible or ultraviolet light.

Photothermal ablation previously has been explored for melanoma, but because it also affects healthy tissue, dose duration and volume have been limited.

Research methods

The researchers packaged hollow, spherical gold nanospheres with a peptide that binds to the melanocortin type 1 receptor, which is overly abundant in melanoma cells.

They first treated melanoma cells in culture. Then, they injected targeted and untargeted nanospheres into mice with melanoma and applied near-infrared light.

Primary results

In cellular studies:

Targeted nanospheres penetrated and embedded in melanoma cells. All the cells were killed or irreparably damaged by near-infrared light.

Non-targeted nanospheres did not penetrate and embed in melanoma cells. Few cells were killed or damaged.

In mouse studies:

Targeted nanospheres gathered in tumors and were distributed throughout them. Smaller amounts were found in the liver and spleen. Compared to melanomas treated with non-targeted nanospheres, they were:

Damaged eight times more by heat

Destroyed with an 88% lower laser dose

Untargeted nanospheres gathered mainly in the spleen, then in the liver and then the tumor. Those in the tumor accumulated near the tumor's blood vessels.

Additional results

In another group of mice, near-infrared light beamed into tumors destroyed:

66% of tumors treated with targeted nanospheres

8% of tumors treated with untargeted nanospheres

What’s next?

"Clinical implications of this approach are not limited to melanoma," Li says. "It's also a proof of principle that receptors common to other cancers can be targeted by peptide-guided hollow gold nanospheres."